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Abstract

We report a method for continuous tuning of ultraviolet (UV) radiation of second harmonic generation in a dispersive beta barium borate (BBO) whispering gallery mode resonator. The doubly resonant enhancement in a high quality factor resonator leads to high conversion efficiency but the resonator dispersion severely limits practical tuning range. By simultaneously varying the temperature of the resonator and the mechanical stress on the disk, we were able to experimentally demonstrate a continuous tuning range of 70 GHz of 317 nm laser light at 0.74%/mW conversion efficiency. The achieved tuning range is at least 35 times wider than that by either mechanical or temperature tuning alone.

(a) Schematic of doubly resonant condition: left, optimized; right, not optimized, where red curves indicate the pump while magenta curves the second harmonics which have wider width due to larger Rayleigh scattering loss at shorter wavelength; (b) Tuning spectra with increasing voltage applied on the piezo as labeled on the curves and with fixed temperature.